The increasing demand for lightweight construction concepts in automotive engineering lends prominence to the use of sandwich sheets which between two thin metallic cover layers have a thermoplastic plastics layer, in order for the potential for saving weight in automotive engineering to be further expanded by using sandwich sheets. Sandwich sheets may have various and mutually exclusive properties which open up new potentials for saving weight. In this way, on account of the plastics layer, sandwich sheets have a significantly lower weight than solid metal sheets and at the same time provide high strength values. Moreover, sandwich sheets are sound absorbing and offer high rigidity. However, it is disadvantageous in sandwich sheets that the latter have an electrically isolating plastics layer which in melt-welding methods causes problems in terms of configuring a flawless welded connection. On account of the inadequate suitability of the sandwich sheets for welding, for example for resistance-welding to other metallic components, sandwich sheets are therefore often adhesively bonded or mechanically joined.
A method for joining a sandwich sheet and a further metallic component, in which the intermediate layer in the connection region is melted and is displaced from the connection region, such that a welded connection may be generated by subsequently establishing electrical contact between the component and the cover layers of the sandwich sheet is disclosed in the German unexamined and first patent publication DE 10 2011 109 708 A1. It is proposed that heating of the joint regions is carried out by electrodes or pressing elements which are capable of being temperature controlled. To this end, the welding electrodes or pressing elements are provided with heating elements, for example. The construction of the welding electrodes thus becomes comparatively complex. Moreover, the speed of heating of the thermoplastic plastics layer may be even further accelerated, such that shorter cycle times may be achieved.
Moreover, a method for resistance-welding two composite sheets, which uses two welding electrodes which are heated and thus heat and displace the plastics layer lying between the cover layers prior to actual welding commencing, is disclosed in US patent document U.S. Pat. No. 4,650,951.
Therefore, a need exists for devices and methods for resistance-welding sandwich sheets and a respective device by way of which a joint between a sandwich sheet and a further component may be provided at low cycle times.